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Garth's own articles

• simple methods for multitasking without a multitasking OS, for systems that lack the resources for a multitasking OS, or where hard realtime requirements would rule one out anyway
• program structures in 65c02 assembly, through macros   Improve assembly-language productivity and maintainability, and reduce bugs, with, in most cases, absolutely no penalty in run speed or memory.  Absolutely no control is lost.
• Self-modifying code on 65xx

• Large look-up tables for hyperfast, accurate 16-Bit scaled-integer math, including trig & log functions.  You can probably implement them even if your computer is already built up, the address space is full, and your I/O is almost all taken.  See how.  Besides the tables themselves given in Intel Hex files, this section of the website has the following pages:
  • Intro to scaled-integer math, plus ideas for interfacing, and how to look up a value
  • Description of look-up tables, and how to use them
  • Rational-number approximations for scaled-integer math
  • How Intel Hex files work
  • How the Intel Hex files were formed
  
  
• 6502 PRIMER: Building your own 6502 computer  This is actually a set of 22 articles, with many of them applying equally well to other computers too:
  
    1. Intro:  Why a 6502?
    2. Address Decoding
    3. Memory Map Requirements
          plus: Why 6502 goes low byte first
    4. Interrupt Connections: IRQ and NMI
    5. 74xx Logic Families and Timing Margins
          plus: "Do I Need Bus Transceivers?"
          and: Static-Handling Precautions
    6. Clock Generation
    7. Reset Circuits
    8. What Do I Do With the "Mystery" Pins, SYNC, RDY, S.O., Φ1, MLB, BE, and VPB?
    9. Construction: Avoiding AC-Performance Problems
  10. Expansion Buses and Interfaces
  11. Getting More On a Board
  12. Answering Wire-Wrap (WW) Questions and Doubts
  13. What About Custom PC Boards?
  14. I/O ICs
          plus: extra info on 6551 ACIA clocking options
  15. Displays
  16. Where to Buy 65-Family Parts
  17. General Steps For A Successful Project
  18. Program-Writing: Where Do I Start?
          what to put in your .ASM file
  19. Debugging
  20. Tips For Programming the 65(c)02 (some affecting hardware design too)
  21. Basic Workbench Equipment
  22. Circuit Potpourri
  
  
  
• 6502 stacks treatise  6502 Stacks: More than you thought!  This is actually a set of 19 articles plus appendices:
  
  1. definition and very basics
  2. subroutine return addresses and nesting
  3. interrupts (plus link to interrupts primer)
  4. virtual stacks and various ways to implement them
  5. stack addressing, both hardware and virtual
  6. passing parameters, and comparison of methods
  7. having a subroutine find inlined data, using the return address
  8. doing math and other operations by stacks in RPN
  9. RPN efficiency
  10. 65c02's added instructions that are useful in stacks
  11. using RTS, RTI, and JSR to synthesize other instructions
  12. where-am-I routines, for self-relocatable code
  13. a peek at the 816's new instructions and capabilities that are relevant to stacks, and 65c02 code which partially synthesizes some of them
  14. local variables and environments
  15. recursion
  16. enough stack space?
  17. compiling or assembling program structures
  18. stack potpourri
      
  19. for further reading
      
  Appendix A. StackOps.ASM
  Appendix B. 816StackOps.ASM
  Appendix C. RPN calculators, a production test application, assembly language, and Forth
  Appendix D. My Problem With the C Programming Language  (You don't have to agree)
  
  
• Circuit Potpourri  This is actually part of the 6502 primer above, but I've been told it needs more attention almost as a stand-alone article.
• article on interrupts.  6502 has outstanding interrupt performance compared to other processors.  Take advantage!  (Enjoy my out-of-date cartoons, too!  :)  )  It's also on 6502.org
• 65c02 interrupt service in high-level Forth, with zero overhead!  (also on 6502.org)
• The 65816 microprocessor: Common Misunderstandings, Plus Attractions
• my project pages on 6502.org.  The workbench computer portion is outdated, so use this page instead for that.  I use it as kind of a Swiss army knife for the workbench.
• "Tip of the Day" column for 6502 development  (42 tips)
• unsigned division of a 32-bit dividend by a 16-bit divisor, resulting in a 16-bit quotient and a 16-bit remainder.  Presented for the 65C02 (with changes for use on 6502) and 65816, with notes of interest to Forth users (for UM/MOD).
• unsigned multiplication (on forum), with 16-bit factors and 32-bit result, correcting a bug in the public-domain 6502 Forth multiplication, as the division article above
• D< bug in common Forths, plus a fix (on forum)
• hex-to-decimal conversion  (There's more discussion on it at this forum topic.)
• quick-n-dirty 8-bit log conversion forum post, with an improvement four posts down from there, and the inverse log function on the next page, here
• Efficient nybble swap on 6502, taking only 8 bytes and 12 clock cycles, and no variables, no stack usage, no look-up table, no X or Y usage.  It uses only the accumulator and status register.
• Assembly Language:  Still Relevant Today
  plus: My feature requests for if you write an assembler
  
• NMOS v. CMOS 6502 differences
• How I got into 6502 and workbench computing
• How I got into Forth
• My workbench computers
  
  
• my slide rules I used in my early years, plus a couple of recent acquisitions of tiny ones (including a working tie-clasp slide rule!)
• How I got into the HP-41cx calculator/computer
• My HP-41 alarms and daytimer program
• My HP-41 program to track time spent on various jobs
  
  
• concise comparison of synchronous-serial interface types (forum post)
• 65SIB spec.  (serial interface bus, compatible with SPI but more flexible)
• SS22 spec.  (6522 synchronous-serial data link between computers)
• I2C-6: proposed hobbyist-friendly connector standard for small I²C modules, suitable for common perfboard
• SPI-10: proposed hobbyist-friendly connector standard for small SPI modules, suitable for common perfboard
• RS-232 primer
  
  
• 6502 v. 65816 code length comparison
  
• 6502 v. PIC16 code length comparisons
• techniques for construction of reliable high-speed digital circuits  (forum topic, with lots of good resources)
• raster graphics on an analog oscilloscope
• 32-bit DO LOOP & related words in 6502 ITC Forth
• ALLOC, FREE, and RESIZE in Forth, for a buffer chain that never gets fragmented
  
  
• Why I do this web site (and why I do it the way I do)
• Things I do and don't like, relating to the computer hobbyist  (You don't have to agree.)
• How to write your résumé  (Take it from someone who had to read a thousand of them and hire a lot of technicians and a few engineers.)
  
  
• my paraffin-and-graphite chain-lube method which gives me 20,000+ miles on a chain and cassette, and keeps itself clean
• a bicycle potpourri, with my early cycling history (brief), plus musings on industry progress, unexpected solutions and facts, physiology, safety, science, terminology, and short stories that are cool, funny, scary, or just interesting
• my first bike trailer, completed Nov 2025
• second bike trailer, bigger than the first, completed in Aug 2026
• need for a bike-friendly society

last updated Nov 4, 2026